The Organic Light Emitting Display (OLED) possesses many outstanding properties of self-illumination, low driving voltage, high luminescence efficiency, short response time, high clarity and contrast, near 180° view angle, wide range of working temperature, applicability of flexible display and large scale full color display. The OLED is considered as the most potential display device.
The OLED can be categorized into two major types, which are the passive driving and the active driving, i.e. the direct addressing and the Thin Film Transistor (TFT) matrix addressing. The active driving is also called Active Matrix (AM) type. Each light-emitting element in the AMOLED is independently controlled by TFT addressing. The pixel driving circuit comprising the light-emitting element and the TFT addressing circuit requires the conductive line to load the OLED cathode voltage (OVSS) for driving.
With the progress of time and technology, the large scale, high resolution AMOLED display device has been gradually developed. Correspondingly, the large scale AMOLED display device requires panel of larger scale and pixels of more amounts. The length of the conductive line becomes longer and longer, and the electrical resistance becomes larger. Unavoidably, the cathode voltage will generate the IR Drop on the conductive line. The electrical resistance value of the conductive line makes that the cathode voltage obtained by each pixel driving circuit is different. Thus, with the same input of the data signal voltage, different pixels have different currents, brightness outputs to result in that the display brightness of the entire panel is nonuniform, and image is different.
Specifically, referring to FIG. 1, the AMOLD display device according to prior art comprises: a substrate 10, a plurality of sub pixels arranged on the substrate 10 in array and a plurality of cathode voltage (OVSS) lines 20 which are in parallel spaced arrangement on the substrate 10, wherein each row of sub pixels is correspondingly coupled to one cathode voltage line 20 to be provided with the cathode voltage by the corresponding cathode voltage line 20. The cathode voltage is inputted to the cathode voltage line 20 from two ends of the cathode voltage line 20 at the borders of the substrate 10. Since the IR Drop due to the resistance of the cathode voltage line 20 will lead to that the actual voltage at the middle of the cathode voltage line 20 is smaller than the voltage inputted to the two ends of the cathode voltage line 20. Namely, the cathode voltage received by the sub pixels at the middle of the substrate 10 is smaller than the cathode voltage received by the sub pixels at two ends of the substrate 10, which ultimately results in the display brightness nonuniformity of the entire panel.